Glycine- and Alanine-Intercalated Layered Double Hydroxides as Highly Efficient Adsorbents for Phosphate with Kinetic Advantages

Abstract

Phosphate is the main cause of eutrophication. Layered double hydroxides (LDH) are considered to be promising phosphate adsorbents due to their high affinity and large capacity. In this study, we partially intercalated zwitterionic glycine and alanine into Cl-LDH (corresponding to MgAl-LDH with interlayer anion Cl−) and synthesized efficient inorganic–organic nanohybrids for phosphate removal with kinetic advantages. Gly-Cl-LDH, Ala-Cl-LDH and Cl-LDH were characterized, and their phosphate adsorption performances under the influence of environment factors (e.g., solution pH, coexisting anions, contact time and phosphate concentration) were investigated. The results show that Gly-Cl-LDH and Ala-Cl-LDH had larger specific surface areas and larger interlayer spaces than Cl-LDH, and exhibited better adsorption performance at a lower pH and better adsorption selectivity against SO42−. Kinetic experiments indicated that Gly-Cl-LDH and Ala-Cl-LDH can reduce phosphate concentrations to a lower level in a shorter time. The pseudo-second-order kinetic constants of Gly-Cl-LDH and Ala-Cl-LDH were 1.27 times and 3.17 times of Cl-LDH, respectively (R2 > 0.996). The maximum adsorption capacities derived from a Langmuir model of Cl-LDH, Gly-Cl-LDH and Ala-Cl-LDH are 63.2 mg-P/L, 55.8 mg-P/L and 58.2 mg-P/L, respectively, which showed superiority over the prevailing phosphate adsorbents. This research provides highly efficient adsorbents for removing phosphate from aqueous solutions.